1. Field of the Invention
This invention relates to a hinge mechanism for a portable apparatus such as a computer or word processor, and more particularly to a hinge mechanism for coupling a foldable flat panel display to a keyboard base of the apparatus.
2. Description of the Related Art
Apparatus such as personal computers and word processors have been recently miniaturized to a portable size which can be conveniently hand-held. These miniaturized apparatus provide the advantage of convenient transport and reduced storage space. They comprise a flat-panel display unit, such as a liquid crystal display or a plasma display, hinged to a keyboard base so that the display unit can be pivoted between an open (angled) position for use and a closed (folded) position for transport or storage. In the open position, the display unit is disposed at an angle of up to 135 degrees to the keyboard base and in the closed position the display unit overlies the keyboard base so it can be carried like an attache case.
Since these apparatus are designed for portability, the display unit is constantly being opened and closed. Therefore, the significance of the mechanism hingedly connecting the display to the keyboard base cannot be understated.
The hinge mechanisms of the prior art comprise a spring which directly generates a contraction force resulting from the spring winding to maintain the display unit in its upright position. The spring is disposed longitudinally to the base and generates a force in this direction. The force exerted by the spring provides the clamping force for maintaining the display in its desired angled position for use.
A significant drawback of these prior hinge mechanisms is that the repeated opening and closing of the display unit weakens the spring, thereby resulting in the display unit abruptly falling onto the keyboard under force of its own weight and causing damage to the apparatus. Moreover, repeated opening and closing of the display eventually results in wearing out the spring so that it no longer effectively functions to support the display unit in its open position. Clearly, these drawbacks are critical since the objective of the portable apparatus is to allow for repeated opening and closing of the display unit to facilitate transport. Accordingly, these drawbacks cannot be avoided by limiting the frequency which the display is opened since this would defeat the objective of providing a compact, portable apparatus.
Attempts have been made to overcome the problems described above, but these attempts have been unsuccessful. One approach to prevent the display unit from undesirably falling onto the keyboard under the gravitational force of its own weight is to increase the rigidity and the strength of the spring mechanism. However, increasing the strength of the spring disadvantageously results in a corresponding increase in the difficulty in opening and closing the display unit. This problem is compounded since the larger the angle of the display with respect to the base (i.e. the greater the opening), the greater the force required by the user to open and close the display unit. This is a ma]or disadvantage to users. Consequently, attempts to overcome the problems of worn springs by providing a stronger spring mechanism is not feasible since it runs counter to the objective of providing convenient opening and closing of the display.
The need therefore exists for a hinge mechanism of sufficient strength which enables the easy opening and closing of the display unit and does not wear out from frequent use.